The goal of the animal core facility is to support the experimental efforts of the different investigators of this proposal, by providing them with a reliably supply of well-characterized. The mice that this core will breed and/or maintain will include mice genetically deficient in fVIII, due to a targeted disruption of either exon 16 or exon 17 of the fVIII gene (henceforth referred to as X-16 and X-17 mice); double mutant mice carrying a disruption of both the fVIII gene and of the gene of either interleukin-4 (IL-4) or IL-12; and wild-type C57Bl/6 mice, to serve as controls. Random samples of the mice will be routinely checked to ensure absence of wild-type genes in the strains carrying disruptions of the fVIII or cytokine genes. This will be done by PCR of blood samples of the individual mice, using suitable primers. Also, we plan to identify any presence of truncated fVIII products in X-16 and X-17 mice using Western blots of mouse blood and sequence-specific anti-fVIII antisera.